Activin a inhibits foam cell formation and up-regulates ABCA1 and ABCG1 expression through Alk4-Smad signaling pathway in RAW 264.7 macrophages

Background: Activin A has been reported to play important roles in the pathogenesis of atherosclerosis. The purpose of this study is to investigate the effects of Activin A on oxidized low-density lipoprotein (ox-LDL)-induced foam cell formation and explore the underlying molecular mechanisms in murine macrophage-like cell line RAW 264.7.

Methods: The effects of Activin A on Dil-labeled ox-LDL uptake were examined by confocal microscopy and flow cytometry analysis. The mRNA and protein levels of Cholesterol receptors were analyzed by RT-qPCR and western blot analysis, respectively. To investigate whether activin receptor-like kinase 4 (ALK4) is required for activin A-mediated cellular effects, cells were pre-treated with SB-431542. The involvement of SMAD2, SMAD3 and SMAD4 was confirmed by transfection with specific small interfering RNAs (siRNAs).

Results: Activin A inhibits ox-ldl-induced foam cell formation and class A scavenger receptors (SR-A) expression, while up-regulates ATP-binding cassette transporter A1 (ABCA1) and ABCG1 expression in RAW 264.7 macrophages. Pre-treatment with SB-431542 abolished activin A-mediated anti-atherogenic effect. Knockdown of SMAD2 reversed activin A-induced inhibition of ox-LDL uptake and SR-A expression. However, knockdown of SMAD3 or SMAD4 did not have such effect. Meanwhile, knockdown of either SMAD2, SMAD3 or SMAD4 reversed the activin A-induced up-regulation of ABCA1 and ABCG1.

Conclusions: Our study provides novel evidence that Activin A may exert anti-atherogenic effects through Alk4-Smad signaling pathway in RAW 264.7 macrophages.

Activin A; Cholesterol efflux; Foam cell formation; Macrophages; Smad signaling pathway.